156 TOPOGRAPHICAL ANATOMY OF THE 



and the perpendicular part of the palatine. It communicates with the 

 maxillary sinus by a large opening immediately below the labyrinth of 

 the ethmoid. 



Disi<ectioti.. — If the lateral wall of tlie iiifiaorhital canal be removed, 

 the branches of the infraorbital nerve and the arteries to the teeth may 

 be exaniineil. 



N. IXFKAOHBITALIS. — Just before it enters the infraorbital canal 

 the nerve furnishes several small branches that, piercing the wall of the 

 maxillary tuber, supply the last cheek-tooth and part of the mucous 

 membrane lining the maxillary sinus. The rest of the cheek-teeth 

 receive branches that leave the nerve while it is within the canal. The 

 canine and incisor teeth are supplied by anterior alveolar lumi, which 

 gain the roots of the teeth by the narrow anterior alveolar canal that 

 leaves the infraorbital canal near its anterior end. 



The nerve, after it has left the canal by the infraorbital foramen, 

 was examined in connection Avith the other structures of the face 

 (page 41). 



A. INFKAORBITALIS. — The infraorbital artery, a branch of the 

 internal maxillary, has been noted as entering the infraorbital canal by 

 the maxillary foramen, after contributing a malar branch that runs 

 along the floor of the orbit. A small branch that leaves the infra- 

 orbital foramen to anastomose with the lateral nasal and superior labial 

 arteries, has also been dissected. 



Small ^posterior alveolar a/deiies (aa. alveolares posteriores), for the 

 supply of the cheek-teeth, leave the infraorbital artery within the 

 canal, and anterior alveolar arteries (aa. alveolares anteriores) gain 

 the canine and incisor teeth by the anterior alveolar canal. 



The organ of hearing (Organon auditus). — The organ of hear- 

 ing is susceptible of a natural division into three parts: The external 

 ear or auricle (auricula), the middle ear or cavity of the tympanum, and 

 the internal ear. The external ear is provided with a skeleton of 

 cartilages, which, with the muscles that move them, have been 

 examined at a previous stage of the dissection (page 26). The canal 

 contained in the external ear is the external acoustic 'meatus (meatus 

 acusticus externus), and is continued beyond the limit of the cartilag- 

 inous skeleton into the temporal bone. The meatus ends at the 

 membrana tympani, by which its cavity is separated from that of the 

 tympanum. 



Dissection. — To make a satisfactory examination of the tympanum 

 and internal ear it is necessary to have several specimens, so that sections 

 across some of them may be made with a fine saw, while one at least is 

 to be examined after piecemeal removal of parts of the bone. From all 



